Keyless entry devices that lock and unlock vehicle doors in a non-contact manner by sending a wireless signal including an ID (identification code) from a remote control terminal are becoming increasingly used as remote controllers for vehicles.
With such a keyless entry device, when a vehicle receives a signal from a remote controller it compares the ID included in such signal with a registered ID, and if the two match, doors are unlocked, allowing keyless entry into the vehicle. To indicate that an operation such as this door unlocking has been properly performed in response to the instructions from the remote controller, an answer back sound, such as from a buzzer, is produced.
Such a keyless entry device has been disclosed, for example, in Japanese Laid-open Utility Model Application 5-30377.
However, for an answer back sound of a conventional keyless entry device, control is merely of a drive and non-drive of a buzzer, producing only a monotone with a frequency set, for example, at 4 kHz. When the surrounding environment is noisy this can be difficult to hear.
Increasing the volume is a conceivable measure for this, but this will cause a different problem of being too loud when a person is near the vehicle or when the surrounding environment is quiet.
A variable answer back sound would be an effective measure for this, but this would cause the problem of high cost, because for this, conventionally, a special IC has been needed.